Ru Decoration By PEALD for Bifunctional Oxygen Electrocatalysis in Solid Oxide Cells

Abstract

Solid oxide cells (SOCs) are electrochemical devices that have garnered significant attention due to their high efficiency, fuel flexibility, and reversibility for operation in both fuel cell and the electrolysis modes. However, the relatively high operating temperature (typically > 800 °C) required presents various challenges such as fast degradation, high operating costs, and slow start-up. To overcome these issues, significant efforts have been made to decrease the operating temperature, but this causes a dramatic decrease in performance due to the low catalytic activity of typical electrode materials. One strategy to increase the catalytic activity is to introduce highly active nanoparticles onto a conventional electrode backbone, but while noble metals such as Ru and Ir have been utilized as oxygen evolution reaction (OER) catalysts, their widespread application in SOECs is hindered by their high cost and limited availability.In this presentation, we demonstrate a highly effective approach to enhance air electrode performance through the deposition of an ultrathin layer of metallic Ru, as thin as ∼7.5 Å, onto (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF) using plasma-enhanced atomic layer deposition (PEALD). The Ru-decorated cell exhibited a current density of 656 mA cm–2 at 1.3 V, significantly outperforming a bare cell (440 mA cm–2 at 1.3 V). The decorated cell also showed a largely enhanced cell durability, which is ascribed to the beneficial role of SrRuO3 that emerges from the reaction between PEALD-based Ru and surface-segregated Sr species, in suppressing Sr segregation and maintaining favorable oxygen desorption kinetics. Further, the PEALD Ru coating on LSCF also reduces the resistance to the oxygen reduction reaction (ORR), highlighting the bifunctional electrocatalytic activities for reversible fuel cells. When the LSCF electrode of a test cell is decorated with ∼7.5 Å of the Ru overcoat and tested in fuel cell mode at 700 °C, this results in a current density of 656 mA cm-2 at 1.3 V in electrolysis mode and a peak power density of 803 mW cm-2, corresponding to an enhancement of 49.1% and 31.9%, respectively, compared to the pristine cell.